^what gm said, except that MfgTool (or imx_usb_loader, if you're on Linux) is useless for the Paperwhite - these tools operate on the "USB downloader mode" (yes, that's yet another mode) which can't be entered on the Paperwhite.

Use the fastboot tool.

PS, and SCNR: Yes, this will hopefully teach you to be careful with what you do.

that was exactly what happened to my PW, and the only solution I found was replacing it from Amazon.

Well, no. The solution would have been to use the fastboot tool to get the Kindle out of fastboot mode.

So, just to make sure that I'm understanding this right: you toyed around in the menu of diagnostic mode, without knowing or even caring to know what you were doing, got stuck, and then sent the device back to Amazon for a replacement?

Congratulations. This is one of the reasons why Amazon tries to lock down their devices - because they have to pay for a replacement which is entirely due to user stupidity. Maybe you shouldn't have jailbroken your device in the first place.